There is a considerable interest in the preparation and use of conducting pathways of the nanoscopic scale as the need for miniaturization and heightened signal sensitivity increases. A class of such conducting pathways include conjugated polymers comprising organic and/or inorganic components, e.g. “molecular wires”. Typically, these molecular wire polymers will be incorporated in devices as a film having an extensive intertwined array of individual conducting pathways. Each individual pathway is provided by a polymer chain, or a nanoscopic aggregate of polymer chains.
FIG. 22 shows a schematic diagram of a prior art device 100. Device 100 comprises a polymer film 105 deposited on substrate 101 between electrodes 102 and 103, in which film 105 is capable of conducting charge. An electrical circuit 104 capable of determining the resistance with voltmeter (or ammeter) 107 completes device 100. Polymer film 105 comprises a plurality of individual polymer chains 106 (drawn as straight lines for illustrative purposes—in reality, the chains are often intertwined). Because no individual polymer chain extends between the electrode, charge conduction must occur through film 105 by charge “hopping” between individual chains (e.g. between chains 106a and 106b). A disadvantage in many films, however, is that the presence of bound guests 108, which may impede charge conduction throughout film 105, is not capable of producing as large of chemical signal as is optimal due the presence of a continuum of parallel pathways. In such materials the charge carriers responsible for the charge conduction can taken an alternative path that avoids the impediments introduced by the bound guests.
One application for nanoscopic pathways is a sensor, particularly for sensing specific molecules. Such sensors include receptor sites to bind analytes via molecular recognition. FIG. 23 shows a schematic of a plurality of isolated receptor molecules 120, each comprising a receptor site 124. Prior to binding analyte 126, receptor molecule 120 has a particular “state” schematically represented by open oval 122, which can define an oxidation state, conformation state, etc. In order to detect a binding event, the sensor relies on a change in the state upon binding an analyte. FIG. 23 schematically shows this change in state with receptor molecule 130 which is bound to analyte 126 and has a change in state depicted by blackened oval 123. Receptor molecules 120 which do not bind analyte 126 remain in state 122. FIG. 23 depicts a binding event as an equilibrium between a concentration of bound receptors and receptors prior to binding. Sensitivity of the device is thus determined by the equilibrium constant K(eq)=[Bound receptor]/([Unbound receptor][Analyte]).
The use of conducting polymer films in sensor applications has the potential to increase the sensitivity. FIG. 24 shows a schematic of a polymer film 130 comprising a plurality of individual polymer chains 132. Film 130 spans a dimension 131, which is the dimension between electrodes if incorporated into a device.
FIG. 25 shows a schematic expansion of individual chain 132, in which receptors 142 are incorporated into chain 132 and interspersed between conducting polymer regions 140, i.e. receptors 142 are wired in series. Preferably, the entire chain comprising regions 140 and 142 comprise a continuous conducting pathway. Each receptor has a site 144 with an initial state depicted by open oval 143. Upon binding analyte 146, the state 146 of each receptor site 142 is affected due to the electronic communication existing between each receptor site 142. The result is a large signal amplification. Only a fractional occupancy is required to achieve a collective signal response.
Despite such recent improvements, there still exists a need to improve the signal amplification for sensors requiring even heightened sensitivity. There also exists a need to develop new nanoscopic materials and materials systems.